Ophthalmic drug efficacy is severely limited by non-compliance. Compliance is adversely affected by the reduced comfort, irritation, and transient quality of vision loss, which lasts minutes to tens of minutes, that is common to many drugs. In particular, these adverse effects are caused by suspensions commonly used for highly lipophilic drugs.
The fundamental challenges of ophthalmic delivery vehicles are to improve comfort; minimize visual blur on instillation; increase drug solubility; increase drug residence time and permeation through the cornea to achieve greater intraocular delivery; reduce systemic drug absorption; and cause minimal local adverse effect. Unfortunately these objectives are not met by current ophthalmic formulations.
Artificial tear vehicles may be used for drug solubilization, but do not confer increased drug residence time or offer other efficacy benefits. More viscous artificial tears use high concentrations of viscosity enhancing agents, such as Celluvisc® (Celluvisc is a registered trademark of Allergan, Inc.), high viscosity carboxymethyl cellulose (CMC) 1%—about 350 centipoise (cps) viscosity, and Refresh Liquigel® (Refresh Liquigel is a registered trademark of Allergan, Inc.), a blend of 0.35% high viscosity CMC and 0.65% low viscosity CMC—about 70 cps, but these formulations have prolonged visual blur that may last for 10 minutes or longer, greatly reducing compliance. These artificial tear vehicles also do not leach drug slowly but rather release a lot to drainage.
Gelling agents have been used with some success in increasing drug residence time and improving drug solubility. By definition such agents are instilled as liquid and then almost immediately triggered to a gel phase, where drug residence time is increased and drug release time extended. Timoptic gel (gellan gum), AzaSite® (Azasite is a registered trademark of Insite Vision, Inc.) (polycarbophil, poloxamer), and Besivance® (Besivance is a registered trademark of Bausch & Lomb, Inc.), (polycarbophil, poloxamer), 0.3% alginate Keltrol®) (Keltrol is a registered trademark of CP Kelco U.S., Inc.) are examples of such agents, where polycarbophil-poloxamer gels are commercially known as Durasite® (Durasite is a registered trademark of Insite Vision, Inc.).
However, most gelling agents: 1) increase blur on instillation; 2) cause lid and lash encrusted gel residue; 3) cause irritation/stinging on instillation; and 4) allow substantial active drug to be released systemically and may have systemic side effects. For drugs with minimal systemic side effects, or intended for only acute use of a few days, these issues are somewhat mitigated; but for drugs with higher systemic effect profiles, particularly lipophilic drugs, and more particularly as chronic use drugs, these issues can seriously affect compliance.
Gelling agents experience a phase transition to a highly viscous state, typically achieving 500-1000 cps or more after their transition. Ionic, pH, and thermal triggers are typically used. However the high shear force of each blink breaks up such phase modified films into discrete particles easily drained into the nasolacrimal duct to the nasal turbinates where residual drug may readily enter systemic circulation. Many gelling agents combine poloxamers of various molecular weights with viscosity enhancers or other gelling agents to create the desired phase transition from liquid on instillation to gel. Typically for those formulations using poloxamer without a second gelling agent, poloxamer concentrations of 15% or greater are needed to achieve gel-transition temperatures at body temperature (37° C.).
Patel (Int. J. of Pharm. Chem. Sci., Vol. 1, October-December 2012) describes the use of poloxamer and a viscosity enhancing agent—a low molecular weight, low viscosity hydroxypropylmethyl cellulose (HPMC E50LV) 1.5% with brimonidine, and demonstrates on testing concentrations of poloxamer with the HPMC from 1% to 19%, no clinically useful gelling capacity in vitro below 15%. Given the dilution of tear film, this typically requires about 21% poloxamer to achieve phase transition to gel on ophthalmic instillation. For example, Qian (Drug Dev. And Industrial Pharmacy, 2010, 36(1): 1340-1347) describes an in situ gelling system for methazolamide, a carbonic anhydrase inhibitor (glaucoma), using 21% Poloxamer 407 and 10% Poloxamer 188 to achieve a preferred phase transition to gel. High viscosity gels have been described with similar limitations to in situ gels, specifically trading off the most egregious noncompliance factors of lid and lash residue and viscous lid drag for lesser amounts of both and with less but still substantially prolonged vision blur.
Use of low viscosity agents reverses the predicament. Other compositions attempt to optimize compliance with formulations that have low viscosity agents such that comfort is good, vision is good and surface residue is absent. However, in such formulations, tear dilution is almost immediate, and drug residence time is severely limited versus in situ gels or viscous liquid gels. Therefore, formulations either improve compliance or enhance efficacy but not both. This is often seen with vehicles for dry eye. Refresh Liquigel® at 70 cps and Celluvisc® at 300 cps are such examples where vision blur is noted.
Accordingly, there remains a need for new formulations which produce greater intraocular drug permeation without compliance reducing gel crustation or blurring, and without allowing significant drug to reach systemic circulation.